Many semiconductor circuits include buried magnetic layers. For instance, a magnetic tunnel junction (MTJ) device is a magnetoresistive device whose resistance is programmable and can be set to either a high resistivity or low resistivity state in response to an applied magnetic field. The difference in resistance between these two states is generally referred to as the magnetoresistance (MR) ratio, which can range for instance from less than 10% to several hundred to percent or more, depending on the temperature and materials from which the device is made. A typical MTJ device configuration includes an insulator layer of tunneling oxide sandwiched between two ferromagnetic layers respectively referred to as the fixed and free layers. The direction of the magnetic field in the free layer determines whether the MTJ device is in the high resistivity state or in the low resistivity state. A binary zero can be stored in the MTJ device by changing its resistance to the low resistivity state, and a binary one can be stored by changing its resistance to the high resistivity state. Advantageously, no static power is required to maintain the resistance state once set. If the insulator layer is sufficiently thin, electrons may pass from one ferromagnetic layer to the other via quantum tunneling through the insulator layer. The two ferromagnetic layers of a given MTJ typically exhibit magnetic anisotropy—a directional dependence of their magnetic properties. Depending upon the direction of magnetization of its constituent ferromagnetic layers, a given MTJ may be classified as exhibiting either in-plane magnetic anisotropy or out-of-plane magnetic anisotropy. An in-plane MTJ is one in which the direction of magnetization is along the plane of the two ferromagnetic layers. Conversely, an out-of-plane MTJ is one in which the direction of magnetization is orthogonal to the plane of the constituent ferromagnetic layers. The two ferromagnetic layers may be configured such that their respective magnetizations are aligned either in the same direction—the parallel (P) state, or in opposing directions—the anti-parallel (AP) state.
Regardless of the specific device being fabricated, manufacturing integrated circuitry that includes one or more magnetic layers typically necessitates tight magnetic process control, so as to provide ferromagnetic layers having specific magnetic qualities suitable for a given application. Currently, in order for such magnetic layers to be tested, one has to break a fully processed wafer or otherwise fabricate a representative stack to access or otherwise monitor the magnetic properties of the given MTJ stack. Thus, there is a need for techniques for testing buried magnetic layers of integrated circuits.